Processes for the production of amines by the catalytic reductive coupling of a primary or secondary amine with a nitrile are known and widely used to produce a variety of secondary and tertiary amines. Di(fattyalkyl)alkylamines, and particularly di(fattyalkyl)methylamines, are representative of tertiary amines produced by reductive amination and are of particular value for the production of fabric softeners, hair conditioners, and antistatic agents.
Di(fattyalkyl)alkylamines can be converted to the fabric softeners, etc. via derivatization to the quaternary salt. Tertiary amine functionality is necessary for successful production of these derivatives. In contrast, intermediate mono(fattyalkyl)methylamines and byproduct secondary di(fattyalkyl)amines do not form the desired quaternary salts selectively, and therefore, are unsuited for processing to the desired end product. In addition, the intermediate and the byproduct amine lack the optimum balance of nonpolar (two long chain fattyalkyl groups) and polar (methylamino group) functionality to provide for the production of effective surfactants and antistats.
Representative patents which describe the reductive coupling of nitriles with amines are as follows:
U.S. Pat. No. 5,648,545 discloses the catalytic amination of a wide variety of nitriles by reacting a nitrogen compound such as ammonia, or a primary or secondary amine with the nitrile at temperatures of from about 80 to 250xc2x0 C. and a hydrogen pressure of 1 to 400 bar. The catalytic amination is carried out in the presence of hydrogen and the catalyst is comprised of a reduced copper oxide/zirconium oxide. Alkali metal carbonate is added to the catalyst prior to reaction. An exemplary nitrile includes N-methylaminopropionitrile and representative amines reacted therewith includes mono and dimethylamine.
Canadian Patent 834,244 discloses a process for continuously producing high molecular weight secondary and tertiary amines by reacting high molecular aliphatic nitriles with volatile primary or secondary amines. The fatty acid nitriles have a carbon content from 8 to 22 carbon atoms and include lauryl and stearyl nitrile and the low boiling amines include dimethylamine, diethylamine, etc. The catalyst is an alkali-modified copper-chromium catalyst with the alkylation being conducted at a temperature of 120 to 180xc2x0 C. and 180 to 210 atmospheres hydrogen pressure. Salts of alkali metals used in preparing the alkali-modified catalysts included those of potassium and sodium.
U.S. Pat. No. 5,869,653 discloses a process for the hydrogenation of nitriles to produce primary amines. In the catalytic hydrogenation of aliphatic nitriles, the nitrile is contacted with hydrogen in the presence of a sponge or Raney(copyright) cobalt catalyst employing lithium hydroxide as a promoter. A wide variety o f aliphatic nitriles (C2xe2x88x9230) are suggested as being suited for conversion to the primary amine by reaction with hydrogen.
U.S. Pat. No. 5,847,220 discloses a process for the catalytic hydrogenation of a cyanopropionaldehyde alkyl acetal in the presence of a nickel or cobalt catalyst promoted with alkali metal hydroxide to form aminobutyraldehyde alkyl acetals, i.e., the primary amine derivative of the cyanoalkyl acetals. The background in the patent discloses a variety of processes for the hydrogenation of nitriles, but these processes generally deal with the hydrogenation of the nitrile itself, rather than a reductive alkylation by the reaction of the nitrile with a primary or secondary amine.
U.S. Pat. No. 5,557,011 discloses a process for producing diamines by reductive coupling of secondary amine with an aliphatic nitrile. In the background of the art, palladium/carbon catalysts were used as the primary reductive coupling catalyst. The improvement in the process wherein palladium is used as a catalyst resided in utilizing an oxidic support, such as a gamma alumina, silica, titania, zirconia, etc. which may be modified by inclusion of up to 15 wt % metal oxides of subgroups IB-VIIB, or Group VIII of the periodic table. Preparation of di-tert-amines from the corresponding dinitriles and secondary amines with palladium supported on an oxide (specifically, on an oxide selected from the group consisting of xcex3-alumina, silica, titania, or zirconia) or on an oxide treated with an alkali metal/alkaline earth oxide is shown.
U.S. Pat. No. 5,894,074 discloses a process for the preparation of tertiary amines from nitriles and secondary amines utilizing a palladium catalyst. The improvement in the process utilizing palladium as a catalyst or catalysts incorporating small amounts of calcium oxide, alumina, magnesium oxide, etc., resided in the inclusion of a small amount at least one further metal selected from the group of 1B and Group VIII, as well as cerium and lanthanum on a support. Examples of the latter class of catalysts include 0.5 wt % palladium/alumina with 20% calcium oxide and 1.0 wt % palladium/alumina with 20% magnesium oxide.
This invention pertains to an improvement in a process for the formation of di(fattyalkyl)alkylamines, and particularly, di(fattyalkyl)methylamines, wherein a fatty nitrile is reacted with a primary alkylamine in the presence of a heterogenous metal reductive amination catalyst and hydrogen. The improvement resides in effecting the reaction in the presence of an effective amount of an acidic promoter, preferably a solid acidic promoter having a pK of less than or equal to about 2.
There are numerous advantages associated with the improved process and these include:
an ability to produce di(fattyalkyl)alkylamines in high selectivity and at high production rates;
an ability to produce di(fattyalkyl)alkylamines in a single step;
an ability to produce a reaction product having a minor portion of byproduct mono(fattyalkyl)alkylamine thereby facilitating separation of the product di(fattyalkyl)alkylamine, from the mono(fattyalkyl)alkylamine;
an ability to effect reductive coupling of two equivalents of a fatty nitrile with a primary amine to produce the corresponding mixed tertiary amine and minimize or avoid coproduction of the corresponding fatty di/trialkylamines;
an ability to reductively aminate a wide range of nitriles; and,
an ability to use the catalyst over an extended time.
This invention pertains to a selective single step process for the reductive amination of nitriles to produce tertiary amines, especially fatty (xe2x89xa6C8) nitriles, by reaction of the corresponding nitrile with a primary amine. This process chemistry comprises reacting two moles of a fatty nitrile with a primary amine through the intermediacy of the mono(fattyalkyl)methylamine followed by in situ reductive coupling with another mole of fatty nitrile to produce the di(fattyalkyl)methylamine.
The single step catalytic reductive amination is described in Equation 1. 
Selectivity problems can occur in the above reaction. It is believed that selectivity to the di(fattyalkyl)alkylamines often suffers because of (a) failure to effect a second reductive coupling with the reductively coupled methylamine or (b) generation of an alternate byproduct. The alternate byproduct is believed to be formed owing to a competing reaction pathway: (a) reduction of the nitrile to the corresponding primary amine, and (b) subsequent coupling of that amine with a second equivalent of nitrile to generate a secondary di(alkyl)amine. The perceived pathway to this alternate byproduct is described by Equation 2. 
The objective is to minimize alternate byproduct formation set forth by equation 2.
In the practice of the process, a wide variety of nitriles may be used in the reductive amination process, and these nitriles include C2+30 aliphatic and aromatic nitriles. Specific examples of nitriles include:
aliphatic nitriles such as acetonitrile, propionitrile, butyronitrile and valeronitrile; ether nitriles such as ethoxypropionitrile, methoxypropionitrile, isopropoxynitrile, biscyanoethylether, bis-(2-cyanoethyl)ethyleneglycol, bis-(2-cyanoethyl)diethyleneglycol, mono-(2-cyanoethyl)diethyleneglycol, bis(2-cyanoethyl)tetramethylene glycol; fatty nitriles, preferably C8xe2x88x9220 fattyalkyl nitriles, saturated and unsaturated, e.g., lauronitrile, cocoalkyl nitrile, oleonitrile, tall oil fatty acid nitrile and stearonitrile; dinitriles such as adiponitrile, methylglutaronitrile and succinonitrile;
xcex2aminonitriles formed by the reaction of acrylonitrile with C1xe2x88x9230 alkylamines and C1xe2x88x928 alkanolamines such as xcex2-aminopropionitrile, di-(2-cyanoethyl)amine, N-methyl-xcex2-aminopropionitrile, N,N-dimethyl-xcex2-aminopropionitrile, N-(2-cyanoethyl)ethanolamine, N,N-di-(2-cyanoethyl)ethanolamine, N-(2-cyanoethyl)diethanolamine and N-(2-cyanoethyl)propanolamine;
xcex2-cyanoethylated amides such as those represented cyanoethylated acetamide and cyanoethylated propionamide; and,
aromatic nitriles which may be used in the process include: benzyl cyanide, benzonitrile, isophthalonitrile and terephthalonitrile.
However, the preferred nitriles are the fatty nitriles having from 8-18 carbon atoms.
A wide variety of primary amines may be used in the reductive amination process. Representative amines which can be used in the reductive amination process are represented by the formula Rxe2x80x2NH2 where Rxe2x80x2 is lower alkyl having from (C1 to C8) carbons or aryl. Examples of candidate amines include primary amines such as monomethylamine, monoethylamine, monopropylamine, diamines such as ethylenediamine, propylenediamine, N-ethylethylenediamine, alkanolamines such as, ethanolamine, ether amines such as methoxypropylamine, methoxyethylamine, ethoxyethylamine, aryl amines such benzyl amine and cycloaliphatic amines such as cyclohexylamine. Preferred amines are the primary C1xe2x88x924 alkylamines, specifically methyl and ethyl amine.
Palladium is the heterogenous reductive amination catalytic metal of choice for the reductive amination reaction. Typically, the reductive amination catalyst is carried upon a heterogeneous support for ease of removal from the reaction medium. Representative supports include carbon, alumina, silica, kielsulghur, and the like. The heterogeneous catalytic metal component, palladium, is carried on the support in an amount usually ranging from about 2 to 20% by weight and preferably from 3-10% and most preferably from 4 to 6% by weight. Other metals such as ruthenium, rhodium, cyanoethyl)ethanolamine, N,N-di-(2-cyanoethyl)ethanolamine, N-(2-cyanoethyl)diethanolamine and N-(2-cyanoethyl)propanolamine;
xcex2-cyanoethylated amides such as those represented cyanoethylated acetamide and cyanoethylated propionamide; and,
aromatic nitriles which may be used in the process include: benzyl cyanide, benzonitrile, isophthalonitrile and terephthalonitrile.
However, the preferred nitriles are the fatty nitriles having from 8-18 carbon atoms.
A wide variety of primary amines may be used in the reductive amination process. Representative amines which can be used in the reductive amination process are represented by the formula Rxe2x80x2NH2 where Rxe2x80x2 is lower alkyl having from (C1 to C8) carbons or aryl. Examples of candidate amines include primary amines such as monomethylamine, monoethylamine, monopropylamine, diamines such as ethylenediamine, propylenediamine, N-ethylethylenediamine, alkanolamines such as, ethanolamine, ether amines such as methoxypropylamine, methoxyethylamine, ethoxyethylamine, aryl amines such benzyl amine and cycloaliphatic amines such as cyclohexylamine. Preferred amines are the primary C1xe2x88x924 alkylamines, specifically methyl and ethyl amine.
Palladium is the heterogenous reductive amination catalytic metal of choice for the reductive amination reaction. Typically, the reductive amination catalyst is carried upon a heterogeneous support for ease of removal from the reaction medium. Representative supports include carbon, alumina, silica, kielsulghur, and the like. The heterogeneous catalytic metal component, palladium, is carried on the support in an amount usually ranging from about 2 to 20% by weight and preferably from 3-10% and most preferably from 4 to 6% by weight. Other metals such as ruthenium, rhodium, copper, and platinum offer little in the way of enhanced selectivity and reaction rate as compared to palladium.
The loading of heterogenous reductive amination catalyst, and particularly the palladium catalyst including support, in the process is the same as the loading level (Pd level of from 3-6 wt % based on the weight of Pd plus support) commonly used in prior art processes, e.g., from 0.1 wt % to 5.0 wt %, dry weight basis, based upon the nitrile feed. Preferred levels range from 1 wt % to 3 wt % of the supported palladium catalyst, dry weight basis, with respect to the nitrile feed.
The mole ratio of nitrile to amine employed in the process may be within a range of 1.5 to 2.5 moles nitrile per mole of primary amine. Obviously, to produce di(fattyalkyl)alkylamine in complete conversion there must be 2 moles nitrile per mole amine. It is possible to use less than 2 moles nitrile per mole amine but the reaction product will contain a mixture of mono and di(fattyalkyl)alkylamine. Normally, a slight excess of nitrile is used to insure complete reductive coupling to the di(fattyalkyl)alkylamine.
A key to effectiveness of the reductive amination process lies in the use of an effective amount of an acidic promoter. By effective amount it is meant that amount of an acidic promoter, preferably solid phase, to promote conversion to the di(fattyalkyl)alkylamine as compared to a non-promoted process. The preferred acidic promoters are ones having a pK of less than or equal to about 2 relative to water. For reasons of efficiency in processing, a solid phase acidic material is used as the promoting agent. When a solid phase acidic promoter is employed, not only must the promoter have the desired acidic pK, it should have a sufficiently large pore size, if it is in the form of a zeolite cage structure, to permit the reactants and product to enter and leaved the cage structure. For example, small pore size zeolites may not accommodate the large size of the di(fattyalkyl)nitrile even though they have the desired acidity.
Examples of acidic promoters include the hydrogen or H form of zeolites which is embraced by acidic montmorillonite, such as K-10 montmorillite, mordenite, X or Y zeolites, dealuminated mordenite and dealuminated X or Y zeolites which have high acidity values but also larger cage structures than the nondealuminated mordenites and zeolites from which they are derived. Other solid acids include sulfonated acidic ion exchange resins such as sulfonated styrene/divinyl benzene resins sold under the trademark Amberlyst(copyright). Aluminosilicates, sulfated oxides such as sulfated zirconia or sulfated niobia, and cesium-promoted phosphotungstic acid also are examples of solid phase acidic promoters. Liquid phase acids may be used as a promoter but they are not easy to separate from the reaction medium. Examples include sulfuric acid, methane sulfonic acid and toluene sulfonic acid.
The level of promoter employed is that which is effective for promoting conversion to the di(fattyalkyl)alkylamine. Typically the acid will be provided to the reaction medium in an amount of from 0.1 to 3 and preferably from 1 to 2 grams per gram catalyst. Levels of solid acid phase promoters above about 3 grams per gram of catalyst, including support, do not offer significant advantages.
A class of polar solvents which are particularly suited for use in the reductive amination process are the lower C1-C6 alkanois and particularly methanol, isopropanol, butanol, and so forth. Tetrahydrofuran and a variety of ethers such as diethyl ether may be used. Typically, the solvent is added in a proportion of about 10 to 1000%, preferably 25 to 200% by weight of the nitrile to be added to the reaction medium. Amounts larger than 200% simply expand and exacerbate the recovery problem. Of the solvents, isopropanol is a preferred solvent as it is economic and also enhances the dissolution of hydrogen therein to maintain catalyst activity during the reductive amination process.
The reduction of the nitrile to the amine is carried out under a hydrogen pressure of from 50 to 2000 psig, typically from 400 to 600 psig, and at temperatures of from about 75 to 100xc2x0 C., typically 100 to 160xc2x0 C. Typical batch reaction times range from 15 to 600 minutes.